1. Field of the Invention
The present invention relates to a resin laminate, and more particularly, to a multilayer resin laminate in which a gas barrier resin layer made of a saponified ethylene-vinyl acetate copolymer or a polyamide resin is adhesive bonded to a selected specific thermoplastic resin layer using an adhesive polymer layer made of a specific modified polyolefin compound.
2. Background Art
Although a polycarbonate resin (hereinafter referred to as a PC) exhibits excellent transparency, heat-resistance and mechanical strength, it does not show a practically sufficient level of moisture impermeability or oxygen barrier properties.
It has therefore been proposed to overcome these drawbacks of the PC while making best use of the advantages thereof by laminating a PC on a resin exhibiting complementary characteristics, such as a polyolefin exhibiting excellent moisture impermeability or a saponified ethylene-vinyl acetate copolymer exhibiting excellent oxygen barrier properties.
This technique has been examined positively particularly in the field of co-extrusion or co-injection molding which ensures effective manufacture of laminates or in the drawing process carried out subsequent to the co-extrusion or co-injection process.
It has been described in, for example, Japanese Patent Laid-Open Nos. 52-125588 and 52-32078, that a polyolefin graft modified by an unsaturated carboxylic acid or a derivative thereof shows excellent adhesion to the PC.
However, the above-described technique has a drawback in that the initial adhesive strength of the polyolefin to the PC is as low as from 150 to 200 g/10 mm, as has been stated in the aforementioned specification.
In other words, a high performance adhesive resin is not known which is capable of firmly adhesive bonding the PC to a saponified ethylene-vinyl acetate copolymer when they are laminated on top of the other by co-extrusion or co-injection molding. Therefore, the production of laminates which could be employed in a wide range of applications is still impossible.
Chlorine resins, e.g., vinyl chloride resin, exhibit excellent resistance to solvents, water resistance, acid resistance, alkali resistance and flame resistance and are thus used in various application fields as food containers and packing materials. However, the oxygen barrier properties of chlorine resins are not at a practical level.
Attempts have therefore been made to overcome the drawbacks of chlorine resins, such as vinyl chloride resin, while making best use of the advantages thereof by laminating it on a resin exhibiting complementary characteristics, such as a polyolefin exhibiting excellent chemical resistance or a saponified ethylene-vinyl acetate copolymer exhibiting excellent oxygen barrier properties.
This technique has been examined positively particularly in the fields of co-extrusion and co-injection molding which ensures effective manufacture of laminates or in the drawing process carried out subsequent to the co-extrusion and co-injection process.
However, a high performance adhesive resin has not been developed which is capable of firmly adhesive bonding the chlorine resin to a resin exhibiting excellent gas barrier properties. For example, in laminating a chlorine containing resin and an ethylene-vinyl acetate copolymer, when a large amount of vinyl acetate in the form of an .alpha.-copolymer with ethylene is introduced so as to improve the adhesion, the mechanical strength of the copolymer is reduced resulting in no improvements in adhesion strength.
Furthermore, a generally employed adhesive polyolefin, .alpha.,.beta.-unsaturated carboxylic acid graft modified or epoxy group containing polyolefin, does not show sufficient adhesion performance to the chlorine containing resin.
Although a thermoplastic polyester resin (hereinafter referred to as a PES) exhibits excellent transparency, heat-resistance and mechanical strength, it does not show a practically sufficient level of moisture impermeability or oxygen barrier properties.
It has therefore been proposed to overcome the drawbacks of the PES while making best use of the advantages thereof by laminating a PES on a resin exhibiting complementary characteristics, such as a polyolefin exhibiting excellent moisture impermeability or a saponified ethylene-vinyl acetate copolymer exhibiting excellent oxygen barrier properties.
This technique has been examined positively particularly in the field of co-extrusion or co-injection molding which ensures effective manufacture of laminates or in the drawing process carried out subsequent to the co-extrusion or co-injection process.
It has been described in, for example, Japanese Patent Laid-Open Nos. 52-125588 and 52-32078, that a polyolefin graft modified by an unsaturated carboxylic acid or a derivative thereof shows excellent adhesion to the PES.
However, the above-described technique has a drawback in that the initial adhesive strength level of the polyolefin to the PES is as low as from 200 to 270 g/10 mm, as has been stated in the aforementioned specifications.
In other words, a high performance adhesive resin is not known which is capable of firmly adhesive bonding the PES to a saponified ethylene-vinyl acetate copolymer when they are laminated on top of each other by co-extrusion or co-injection molding. Therefore, the production of laminates which could be employed in a wide range of applications is still impossible.
Acrylic resins exhibit transparency, excellent weathering resistance, chemical resistance and electric insulation, are light in weight and strong, and show excellent processability. Therefore, acrylic resins have been used in various fields, as forming materials, food containers and packaging materials. However, the oxygen barrier properties of the acrylic resins are not at a practical level.
Attempts have therefore been made to overcome the drawbacks of acrylic resins while making best use of the advantages thereof by laminating an acrylic resin on a resin exhibiting complementary characteristics, such as a saponified ethylene-vinyl acetate copolymer exhibiting excellent oxygen barrier properties.
This technique has been examined positively particularly in the fields of co-extrusion or co-injection molding which ensures effective manufacture of laminates or in the drawing process carried out subsequent to the co-extrusion or co-injection process.
However, a high performance adhesive resin has not been developed which is capable of firmly adhesive bonding an acrylic resin to a resin exhibiting excellent gas barrier properties. For example, in laminating an acrylic resin and an ethylene-vinyl acetate copolymer, when a large amount of vinyl acetate in the form of an .alpha.-copolymer with ethylene is introduced so as to improve the adhesion, the mechanical strength of the copolymer is reduced resulting in no improvement in adhesion strength.
Furthermore, a generally employed adhesive polyolefin, .alpha.,.beta.-unsaturated carboxylic acid graft modified or epoxy group containing polyolefin, does not show sufficient adhesion performance to the acrylic resin.
Styrene resins are stable to heat, exhibit excellent processability, and are characterized by their low hygroscopic property, tastelessness and odorlessness and chemical inactivity. Therefore, styrene resins have been used in various fields, as food containers and packing materials. However, the oxygen barrier properties of the styrene resins are not at a practical level.
Attempts have therefore been made to overcome the drawbacks of styrene resins while making best use of the advantages thereof by laminating a styrene resin on a resin exhibiting complementary characteristics, such as a saponified ethylene-vinyl acetate copolymer exhibiting excellent oxygen barrier properties.
This technique has been examined positively particularly in the field of co-extrusion or co-injection molding which ensures effective manufacture of laminates or in the drawing process carried out subsequent to the co-extrusion or co-injection process.
However, a high performance adhesive resin has not been developed which is capable of firmly bonding a styrene resin to a resin exhibiting excellent gas barrier properties. For example, in laminating an styrene resin and an ethylene-vinyl acetate copolymer, when the proportion of vinyl acetate which forms a copolymer together with ethylene is increased so as to improve the adhesion, the mechanical strength of the copolymer is reduced while the adhesion strength is not improved.
Furthermore, a generally employed adhesive polyolefin, .alpha.,.beta.-unsaturated carboxylic acid graft modified or epoxy group containing polyolefin, does not show sufficient adhesion performance to the styrene resin.